---
title: "stdin-closed: shell commands run with stdin at end-of-file, said once per session"
description: "An advisory by default: it explains, and blocks nothing, on shell commands run with stdin at end-of-file, said once per session."
tags: [guard, rules, stdin-closed, advise]
---

# stdin-closed

An advisory by default: it explains, and blocks nothing, on shell commands run with stdin at end-of-file, said once per session.

## What it catches

Shell commands run with stdin at end-of-file, said once per session.

## Why

An agent's shell command inherits an open stdin nobody writes to, so anything that reads it (grep or cat with no operand, read, a prompt, ssh, a pager) waits forever, and a host that times the call out backgrounds it rather than killing it. A grep whose file operands expand to nothing reads that stdin until the host gives up. Where the host lets a hook rewrite the call, the guard prefixes the command with `exec </dev/null;`, never on a refused call and never twice. A heredoc, a pipe or a `<` still give a command its input, since each sets stdin for its own command. A prefix rather than a `{ <command>` ... `} </dev/null` group: one host's isolation check for worktree agents judges the rewritten line, and it refuses the group as too complex even around `stat` or `git status`, where it refuses the prefix only on a line it already found borderline (runtime-computed values beside a redirect).

## Default and override

By default this rule takes the decision `advise`. A workspace sets it by name, in its root
magusfile, to `deny`, `advise` or `off`:

```buzz
magus\guard.builtins({"stdin-closed": "deny"})
```

A loosening takes effect once it is committed; a tightening applies at once.

## Seeing it

A verdict names its rule in brackets, which is how you got here:

```text
advise [stdin-closed]: ...
```

`magus describe rule stdin-closed` prints the same entry at a terminal, and
`magus describe rules` lists every rule this workspace enforces.

## See also

- [All rules](index.md) - what this workspace enforces, deny first
- [The guard](../../guides/integrations/agents/guard.md) - how a verdict is reached and wired
- [Setting a built-in rule](../../guides/integrations/agents/guard.md#setting-a-built-in-rule) - how a workspace changes this default